The present invention is related to a multi-band radio (wireless) terminal apparatus capable of performing radio communications over a plurality of communication frequencies, and more specifically, to a technique suitable in a portable telephone apparatus.
As the communication system available in U.S.A., there is such a communication system that a single CDMA (Code Division Multiple Access) communication method is applied to different communication frequency bands (800 MHz band and 1.9 GHz band). In such a commutation system, if a radio terminal apparatus is operable in both the communication frequency bands, then this radio terminal apparatus becomes very convenient for users.
Generally speaking, this sort of radio terminal apparatus employs the superheterodyne system. This superheterodyne system is applied to each of communication frequency bands so as to switch an intermediate frequency (IF).
In a CDMA type radio terminal apparatus designed for U.S.A. and operable in both communication frequency bands of 800 MHz and 1.9 GHz, a first local oscillator is commonly used in a signal transmission system and also in a signal reception system so as to frequency-convert a radio signal between a radio communication frequency and an intermediate frequency. In this case, the reception frequency is selected to be higher than the transmission frequency by 45 MHz in the 800 MHz band, whereas the reception frequency is selected to be higher than the transmission frequency by 80 MHz. As a result, in the signal transmission system, 130.38 MHz can be commonly used in both the 800 MHz band and the 1.9 GHz as the intermediate frequency. However, in the signal reception system, two sets of intermediate frequencies are provided. That is, the intermediate frequency of 85.38 MHz is provided for the 800 MHz band, whereas the intermediate frequency of 210.38 MHz is provided for the 1.9 GHz band.
As a consequence, two sets of the reception-sided (RX) intermediate frequency (IF) band-pass filters for the 800 MHz band and the 1.9 GHz band are required as to RX IF band-pass filters. Thus, these RX IF band-pass filters for the 800 MHz/1.9 GHz bands must be selectively operated. In general, these RX IF band-pass filters are required to have the steep filtering characteristics. To this end, since SAW (Surface Acoustic Wave) filters are employed as the RX IF band-pass filters, the employment of these SAW filters would increase the manufacturing cost of this sort of radio terminal apparatus.
The present invention has been made to solve the above-described cost-up problem, and therefore, has an object to provide such a multi-band radio terminal apparatus capable of transmitting/receiving signals in a plurality of radio communication frequency bands, in which reception intermediate frequencies for the respective communication frequency bands are made equal to each other. As a consequence, circuit arrangements provided subsequent to a reception intermediate frequency circuit stage can be commonly used for both the signal transmission/reception systems, and also can be made simple.
To achieve the above-describe object, a multi-band radio terminal apparatus, according to a first aspect of the present invention, is featured by such a multi-band radio terminal apparatus comprising: transmitting/receiving means for processing radio communication signals of a plurality of communication frequency bands, the radio communication signals being used to communicate with a base station; first frequency converting means for frequency-converting the frequency bands of the radio communication signals between the communication frequency bands and an intermediate frequency band; and second frequency converting means for converting the radio communication signals between base-band signals and an intermediate frequency signal; wherein: the first frequency converting means includes: one reception-sided mixer for converting a reception signal within the communication frequency band in to another reception signal within the intermediate frequency band; one transmission-sided mixer for converting a transmission signal within the intermediate frequency band into another transmission signal within the communication frequency band; and a first single local oscillator for commonly supplying a local oscillator signal to both the reception-sided mixer and the transmission-sided mixer; and the first local oscillator includes: switching means for commonly supplying an oscillator output of an oscillator to both the reception-sided mixer and the transmission-sided mixer while maintaining a frequency of the oscillator output, or for either doubling or frequency-dividing the frequency of the oscillator output to commonly supply the oscillator output having either the doubled frequency or the frequency-divided frequency to both the reception-sided mixer and the transmission-sided mixer in response to the frequency band of the radio signal used in the communication between the base station and the multi-band radio terminal apparatus.
Furthermore, a multi-band radio terminal apparatus, according to a second aspect of the present invention, is featured by such a multi-band radio terminal apparatus comprising: transmitting/receiving means for processing radio communication signals of a plurality of communication frequency bands, the radio communication signals being used to communicate with a base station; first frequency converting means for frequency-converting the frequency bands of the radio communication signals between the communication frequency bands and an intermediate frequency band; and second frequency converting means for converting the radio communication signals between base-band signals and an intermediate frequency signal; wherein: the first frequency converting means includes: one reception-sided mixer for converting a reception signal within the communication frequency band into another reception signal within the intermediate frequency band; one transmission-sided mixer for converting a transmission signal within the intermediate frequency band into another transmission signal within the communication frequency band; and a first single local oscillator for commonly supplying a local oscillator signal to both the reception-sided mixer and the transmission-sided mixer; and the second frequency converting means includes: a second local oscillator for producing a second local oscillator signal having a frequency which is varied in response to the frequency band of the radio signal used in the communication between the base station and the multi-band radio terminal apparatus; and a mixer for using the second local oscillator signal so as to convert a transmission base-band signal into a transmission intermediate frequency signal.